Facsimile synchronizing system



Aug.12, 1947. H. E. HALLBORG ETAL 2,425,616 7 FACSIMILE SYNCHRONI Z INGSYSTEM Filed June 19, 1945 5 Sheets-Sheet 1 Ag. l2, 1947. H. E. HALLBORGETAL v 2,425,616

FACSIMILE SYNCHRONIZING SYSTEM Aug; 12, 1947. H. E. HALLBORG ETAL2,425,616

S FACSIMILE SYNCHRONIZING SYSTEM Filed June 19, 1943 3 Sheets-Sheet 3VOL THGE C'OIVTBOL (JN/T A TTO/BNEY Patented ug. 12, 1947 OFFHCE FACSIESYNCHRONIZING SYSTEM of Delaware Application .lune 19, 1943, Serial No.491,537

7 Claims'.

'Ihe present invention relates to communication systems, and moreparticularly to systems for sending and receiving facsimile signals insecrecy. More specifically, the present invention relates to a secretcommunication system wherein variable speed mechanisms are provided atthe transmitting and receiving stations, which mechanisms are caused tohave substantially identical speed variations.

Older privacy systems have one or more of the following limitations;they require inherent change in equipment, require a wide frequency bandfor transmission, intermittent transmission is necessary, power iswasted in spurious signals, critical adjustments are required, thequality of the received subject made is below normal standards.Moreover, these older systems are not suitable because of multi-patheffects where trans- -mission over a long radio circuit is necessary.

The secrecy system disclosed herein may be added to existing equipmentsubstantially without change in the scanning and recording circuits orin the method of transmission normally employed. Secrecy systems inaccordance with the invention are relatively simple in operation andgive a high degree of privacy at a comparatively low cost for equipmentand operation. A system embodying this invention may be operatednormally after performing a simple switching operation at each circuitterminal. No power is wasted unnecessarily in spurious signals.

In brief, the operating speed of both an image or facsimile signalgenerator and an image vor facsimile signal recorder are varied inaccordance with a prearranged plan or code. This may be doneconveniently by a switch or cam at both the transmitting and receivingstations for varying the rotational speed of the mechanical power sourceat arbitrarily selected time intervals whereby unauthorized persons notknowing and having the means for changing the speed of operation oftheir receiver in accordance with the transmitter speed changes cannotsynchronize their receiver to reproduce anything which is intelligible.

The principal object of the present invention is to provide novelmethods of and apparatus for preventing the intelligible reception offacsimile signals by anyone except authorized persons.

Another object of the present invention is to provide a facsimilerecorder having means for varying the degree of departure from normalsynchronous operation in a predetermined manner.

A further object of the present invention is 2 to provide a novelarrangement for obtaining changes in the speed of a facsimile machine inaccordance with a predetermined code.

Other and more specific objects of the invention will become apparentand suggest themselves to those skilled in the art to which theinvention is directed upon reading the following specification andclaims in connection with the drawings in which:

Fig. 1 is a schematic block-diagram of a facsimile transmitting stationembodying the invention;

Fig. 2 is a diagrammatic showing of a receiving station in accordancewith the invention;

Figs. 3 and 4 are side elevational views of details of Fig. 2;

Fig.,5 is a diagrammatic showing of a facsimile station embodying theinvention in a modified form; and

Fig. 6 is a fragmentary view in side elevation of a detail of Fig. 5.

Referring to Fig. 1, there is shown a transmitting station having afacsimile scanner indicated generally by reference character I0, andcomprising a copy holding drum II and a facsimile signal generatingdevice, such as a scanning head I2. The scanning head i2 is advancedaxially of the drum Il by a lead screw I4 driven from the drum shaft I6by a gear and pinion combination i8. It will be understood that thescanner I@ may be of any known type employing either the rotating copyholding drum II, shown by way of example, or a continuous sheet or webin which the signal generatingrdevice i2 reciprocates line by line overthe web. The copy holding drum l I has a message sheet I9 lsecuredthereon in any suitable manner, for example, by a clamping deviceindicated conventionally at 2 I. Facsimile signals representing amessage or picture inscribed or otherwise provided on the message sheetI9 will be generated when the copy holding drum I l is rotated withrespect to the scanning head l2. The drum II and the lead screw l aredriven from a motor 23 through a change speed device such as a gear box24, and, if desired, through a combination 26, shown conventionally, ora worm and worm wheel combination as shown by Fig. 5 of the drawings.The gear box 2t provides a convenient means for changing (usuallyreducing) the speed of the motor 23 to the desired operating speed ofthe scanning drum I I. The motor 23 as will hereinafter appear ispreferably an alternating current synchronous motor.

A conventional radio transmitter 28, comprising the conventionaloscillator and modulator,

3 radiates signals from an antenna 23 which signals contain theintelligence derived from scanning the message sheet i9. It will beunderstood, however, that any communication channel such as a wire line,for example, may be substituted for the radio link 29.

The novel means of this invention for insuring secrecy and now to bedescribed are independent of the conventional facsimile stationequipment just described. A standard frequency source 3l, which servesas a reference frequency for vthe transmitter, is of any suitable typeand .produces a substantially constant tone frequency of the order of600 cycles per second, for example, It will be understood, however, thatany desired tone frequency may vbe employed, although the frequency of600 cycles is herein 'selected and asu sumed as the standard since it isa multiple of the usual power supply frequency of 60 cycles for whichreadily available equipment is manufactured. The output of the standardfrequency source 3l is applied to two frequency dividers and frequencygenerators 33 and 34, which serve in the illustrative example of Fig. 1not only lto produce a sub-multiple of the output frequency of theAstandard source 3| but to change the 'frequency of the sub-multiple inla predetermined manner. For example, the device 33 may .produce afrequency of 60 cycles plus another frequency f. The device 34 mayproduce a frequency of 60 cycles minus the same frequency f.Thisfrequency f is selected to be within the range of stable operatingfrequencies of the motor 23 and may, for example, be 1 per cent yof theselected submultiple of the frequency of the source 3l. Practically anyspeed change may .be utilized up to the limit of synchronous response'bythe motor. The output of the generator and dividers 33 and 34 will thenbe 6l and 59 cycles respectively. The generator and divider devices 33and 34 are connected to switching devices A3'1 and 538 respectivelyvwhich are controlled by a device ywhich may be a code generator 3'9 andpreferably is of the nonrepeating type; that is to say, .the group ofcode pulses produced by the code generator 39 are not repeated in normaloperation during a transmission or a series of transmissions from theradio transmitter 2,8. 'I'he code generator"39 vpreferably providescut-.off bias for the switching devices 31 and 38, and its operation istimed Afrom 4the standard `frequency source 3i through a frequencygenerator and divider lll over a connection 42. It Ywill -be understoodthat the code generator 39 may be connected directly tothe standardsource 3|,.'if desired, rather than to the frequency generator anddivider llc as shown. The code generator-39-maybe a counter controlledor a cam controlledelectronic device, or itmay comprise a rotary cam andswitch such as is shown by Way of example in Fig. 3 of the drawings. Theswitching 'devices 31 and 33 may -be yrepeaters orvampliers biased tocut-on over Vconnections 44 and 46 from the code generator39 orelectromagnetic relays held in an inoperative condition at times by thecode generator. The latter cuts off switching device 31 when switchingdevice v38 is operative and vice versa. The'outputterminals-of theswitching devices 31 and 38 are connected by way-of conductors 0.1 toapair .of terminal studs 49 on adouble throw switch-5l. The Yswitch armsof this switch are connectedby way of an amplier-SZ-tothe scanner drivemotor 23.

q `If desired, the switch 5ly maybe provided with additional switch armsand studs in any well known manner to cut out the code controlledfrquency changing equipment, shown at the top of Fig. 1. When the switcharms of the switch 5I are in their left hand position in contact withstuds 54 to connect the motor and amplifier 52 directly to the ratedmotor frequency source, namely, standard source '3i and divider 40,ordinary operation is obtained so that intelligible copy may be receivedby ordinary receivers within the transmitting range of transmitter 28.It will be understood by those skilled in the art that the source `3|may be a commercial `power source where .the transmitter and receiverscan be connected to the same commercial power network to insuresynchronism. Also, dividers 33, B, and 4] may be a single unit ifdesired.

A description of the operation of the equipment shown by Fig. l inconjunction with a similarly equipped receiving station will bedescribed in detail following a description of Fig. 2 which shows, byway of example, a receiving station equipped ywith apparatus necessaryfor the intelligible reception of signals transmitted b y a transmitterembodying the invention, such, Vfor example, as that shown by Fig.Y l ofthe drawings.

Referring to Fig. 2, reference character '56 indicates a recordingscanner which is or may be similar to the transmitting scanner lil ofFig, 1, the principal difference being that a copying head v51 issubstituted for the scanning head l2 of Fig. 1, Radio signals areintercepted by an antenna 59 connected to a radio receiver 6I. A signalamplier and detector combination 62 serves to amplify picture signalswhich are suppliedto the copying head 51 in known manner. A synchronousmotor 64, which may be similar to the motor 23 of Fig. 1 drives therecorder 56 through a gear and pinion combination 66, shownconventionally, and the Vgear box 61. If desired, a worm and worm wheelcombination, as shown on Fig. 5 of the drawings, may be substitutedYforthe gear and pinion S6.

A standard frequency source suppliesa substantially constant frequencyalternating current voltage to a frequency divider 1i, the output ofwhich is a sub-multiple of the frequency ,produced or `generated by thestandard frequency source 69. The frequency of the standard source mayconveniently be 600 cycles per second vwith the frequency divider havinga ratio of l0 to 1 so that the output of the latter to an amplifier v'i2is 60 cycles, a frequency which is suitable for ope erating asynchronous motor 1,4. This motor-.may be of the small .synchronousclock .drive type which Vis readilyeobtainable commercially. Tione wheelrotors 16 and 1v1 of a pair of induction generators are .carried by ashaft 18 which is driven from the motor 154 through aspeed reducing gearbox 13. The speed at which the shaft 18 is to-be driven depends upon thefrequency of the fout-put .of the induction generators 16 `and -11assuming a given number of teeth on their rotors. The output frequencyof these generators `preferably is such that their output may beamplified in an amplier 8| andapplied to the terminals ofthesynchronousmotor 64. For example, if --the mo-tor 14 is a 60 cycle twopole clockmotor, the speed reducing gear'should have gear ratio ofGOtorr1 so that with-59 teeth on the rotor' kand the 6l teeth on the rotor11,*these two inductor genera,- tors will provide output Vvoltages at 59vand .6l Vcycles respectively which is l lpercent above and 1 per centbelow the frequency of the output of the divider 1l.

The stators of the inductor generators are 5 similar, and generator 16is shown more in detail by Fig. 4 of the drawings. It is seen tocomprise a permanently magnetized yoke 83, and the two polar tips 84 areseparated by a distance equal to several times the pitch of the teeth onthe rotor. A winding 86 surrounds a portion of the magnetic circuit, forexample one of the pole tips, and one of its terminals is connected byway of a conductor 88 to a contact 89 of a. cam operated switch 9| inthe manner shown diagrammatically on Fig. 2 ofthe drawings and more indetail by Fig. 3. The remaining terminal is connected to a conductor 93which connects with one stud 94 of a double pole double throw switch 96.The corresponding stud ofthe switch 96 is connected to the tongue 91 ofthe switch 9| by way of a conductor 99. The winding |02 of the generator11 is connected by a conductor |03 to contact |04 of the switch 9|. Theremaining terminal of the winding |02 is connected to the conductor 93.With the switch 96 in its right hand position, as shown, the receiverwill operate in conjunction with a'transmitter such as the one shown inFig. l to give a legible record.

The cam |01 which operates the cam switch 9| is provided with notches|08 cut in accordance with a predetermined code to match the code of thesimilar device employed at the transmitter, for example, the device 39of Fig. 1.

In operation of the system so far described, the transmitting station,which may be provided with a code Wheel arrangement as shown in Figs. 2and 3 of the drawings or with a code generator 39, as pointed out above,is placed in operation, with a message sheet I9 bearing subject matterfor transmission secured on'the drum of scanner I0. The code generator39 is arranged to operate in accordance with an irregularly occurringcode or, if a cam switch type of code device is employed, the cam isselected so as to have irregularly occurring indentations or,conversely, irregularly occurring teeth. The latter arrangementnecessitates merely a reversal of the cam switch contacts. generatorsare employed, the selective code may be further complicated to preventits solution by an unauthorized party by increasing the number of thetones generated by adding a cam code wheel and cam operated switch perpair of added frequencies. The code generator at the receiver, which maycomprise the cam |01 and the cam operated switch 9|, operates to connecteither the inductor generator 86 or the inductor generator |02 incircuit at the same time as the switching device 31 or the switchingdevice 38 at the transmitter is in circuit. The speed of operation ofthe transmitter scanner I will then correspond at any instant to thespeed of operation of the recording scanner 56, and a legible copy ofthe transmitted subject matter will be recorded.

The apparatus at the transmitting station may be employed to transmit ina normal manner to any receiving station by placing the switch in itsleft-hand position. Likewise, the receiver of Fig. 2 may be employed toreceive signals from; any transmitter station by placing the switch 96in its left-hand position.

Fig. 5 of the drawings discloses a modification.

Vin which the facsimile scanner |I2 is driven by an induction motor II4. This apparatus may beused either at a transmitting or receivingstation. The motor ||4 drives the copy holding drum IIB of the scanner|I2 through gearing ||1 and a worm and worm-wheel combination |I8. The:gearing ||1 also drives a shaft I 2| on which If a cam switch andinductor4 are vmounted the rotors/of inductor generators |22, |23, |24.The shaft |2| also has secured thereto a cam disc |26 which operates acam controlled switch |21. The proper time phase of switching betweenthe inductor generators |23 and |24 is controlled by the switch |21. Acam operated switch |29 is controlled by a code disc |3| having codeteeth cut thereon. This code disc |3| is mounted on a shaft |28 andcorrespends in function to the cam |01 of Figs. 2 and 3 of the drawingsand is driven at reduced speed relative to disc |26 by gearing |30.

The motor I|4 obtains driving power from a suitable alternating currentsource which may be a standard -volt, (iO-cycle yservice outletconnected at terminal points |33. The driving speed of the motor ||4 isvaried in accordance with the code provided on the code disc |3| bymeans of a phase detector |36 and a voltage control unit |31. Thesepieces of apparatus are disclosed and claimed in a copending applicationof Hallborg et al., Serial No. 491,538, filed June 19, 1943. So much ofthe description appearing in this copending application as is necessaryto an understanding of the present invention lwill be repeated hereinfor the sake of completeness of the disclosure. Briefly, the device |36beats the output of the generators |22 to |24 with the output of thestandard frequency source |39 to produce a phase shift in the beat Wave.This phase shift produces a proportional change in resistance in themotor ycircuitI resulting in a proportional change in motor speed.

The standard frequency source |39 provides a regulated frequency outputwhich is fed to the phase detector |36 over a connection |4| andinductor generators |22 to |24 are also connected to the phase detector|36 over a connection |42 under control of a polar relay |44, theoperating coils of which are connected to the contacts of the camoperated switch |29. A suitable source of operating potential |46 inseries with the cam operated switch |21 provides for energization of therelay coils. A manually operable switch |41 interposed in one leg of theconnection |42 provides for operating the system as a privacy system orin the normal manner in conjunction with any type of transmitting orreceiving station. The tongue |48 of the polar relay, when in itsright-hand position (and with switch |41 in the privacy position, asshown), connects the inductor generator |24 to the phase detector |36.This inductor generator |24 is provided with a number of teeth such thatit would generate a frequency higher than the frequency of the frequencystandard |39 if the shaft |2| were permitted to run at normal speed..With the tongue |48 of polar relay |44 in its left-hand position, andthe manual switch |41 in the -position shown,

the inductor generator |23 is connected to the phase detector |36. Theinductor generator |23 is provided with a number of teeth such that itwould generate a frequency lower than the normal operating frequency ofthe motor ||4 if the shaft |2| were permitted to run at normal speed.

The inductor generator |22 is provided with a number of teeth such thatit will generate a frequency equal to the normal operating frequency ofthe motor |I4 when it is operating at normal speed. Therefore, with theswitch |41 in its right-hand position, the motor II4 will operate at aconstant speed under -control of the output of the standard frequencysource |39.

In operation of the apparatus described, the switch |29 will operate toplace either of .the in- -ductor generators |23 or V4Min connection withfthe-phasepetector |36 so as-to supply voltage thereto. -Assumingv-thatthe `code disc 13| .has rnovedth'e switch L29 into the position shownY-t-lfie tong-ue 448 of the polar lrelay will, when switch t2?! closes,:connect-the .-i'nductorz generator |24 to fthe phase detector device|35.. yl2.b.e.mo mentary increase in frequency will :result-in'instantaneous 'decrease .in the ,motorspeed gto .the -point latwhich-the vindulotor. generator |24 generates precisely .standar/dfrequencyloy .reasonr of a decrease in the supply .voltage .applied'toI.the motor I-I4 `througnthe .voltage control unit 431. viii/Then `thecam .code disc causes theswitch vk|23 to `move .to its right-handposition, -the tongue .lfof the polar relay .will `connect 'the inductorgenerator |23 tothe phase detector 1.36. An in- .,s'tantaneous 4increasein the .speed .of the motor 'Ille wiIlJ-be produced andvmaintained.until the :codedisc '|3l again .operatesthe Aswitch '129.The .tongue .1152. o'fthe relay Mil-short circuits aresistor ,|53whichis 'in series with the motor '|14 and assists in obtaining -theAvery rapidirrcrease in speed.

The apparatus described in connection jwith Fig. '5 'is operated in themanner 'already described .in connection .with Figs. l fand 2 'of thedrawings. For example, atth'e transmitter 'station amessage sheet"bearing ja'ccpy fortransmission will be 'placed V'on' the drum ""HBAand a code disc |3I will be selected "and mounted Aon "At the receiver`station a lsuitable -type ormessage blank will be placed'onfthe drum-|f|l6 4and a codeidisc 3| ji'denticalwith ythat'at thetransmittenwillAbe used. `Phasing 'orfrarning Vof the copy may 'be accomplishedinaccordance "with well known methods.

Solely by way of "example-a vtypicalesystemoperated-in`accordancewiththeinventionemployed `a motor |14 with-anormalspeed of 1760 R. P.M.

A gear ratio of '30u (ffl to l) 'was-provided `in 'the .reducing gear,where in '.Was the number rof iteeth in .the .reference 'frequency tone.wheel |122, `f1 'was vthe :standard reference frequency, and 7i-.l and'n+1 :the number of teeth for producing drum-speeds above .andbelownormalrbymeansof in'ductor generatorsY |23 and |24. The drivingirationfthezworm y, and .worm wheel combination I IB .was l to-. 30.The-'driving gear ratio. forthe wormfishaft'wasf45 tof44. .The gear.ratio Ibetween .the motor |-4 .and tnefsbaft |.2| Ain the speciiicexample now-ilbeingydescribed has .already been given.

AHavingnow described our invention, what we Vclaim .as :new .and desireyto nhave protected by Letters .Patentxisz 1. Inan electricalicommunicationsystem comprising a movable .intelligence:transferring-mem- .ber ,and power drive vmeans for saidmovable latingdevice,` analternati-ng kcurrent power source having -an .output :of a.predetermined frequency, asecond alternating .current vpower sourcehaV.- .ing .a ftrequency .dinering `from the frequency of .saidrstnamedsourca .and code operated means V@to ,connectsaid .power drivemeans with eitherof .said .power sources.

'.3.. .A secrecy .system comprising a signal 'translating Adevice,powerdrive means for said translating `device, astable Yfrequency alternating.currentpower source, .an .alternating current ,power source ,having .ia.frequency higher than the fre- .quencynf .said .stable `frequencysource, .an alternating .current :power source .having a frequency lower:than the .frequency of said stable frequency .power source,.code-.operated means tot connect said power drivemeans witheithenofsadsecond cr third ,named :power sources, and means associated.with .said .stable frequency :alternating current powersource forcontrolling ,said code :.operatedrlneans.

4.ln an electrical communication system com- .prising amovableintelligence transferringmernber and power.1drive means Vfor saidmm/able member, Ameans cooperating Y with said member 'to igenerate.intelligence signals, -ia frequency controll'ed electrical power supplyfor said power `drive means, means toproduce aseparate alterablefrequency, means to compare said vseparate frequency with the frequencyof said supply,

Ameans* to `.produce a change in Lspeedof said vpower drive,meansinaccordance with said com'- Kparison, and .code controlled means forcontrol- .ling .said frequency varying means andthereby contrllingfsaidintelligence transferring member lsc .that communication by theintellgencesignals .means,. means1for,providing `a supplementalpowersupply-.havinge Characteristic different from a v.like characteristic ofvthe ,power supply .for said r,powerldrive means, means to compare s aidcharv acteristics.means toproduce a change in the speedof said.powerdrive means as aresult of .said comparison, ,and code controlledmeans for controlling said .supplemental ,power .supply so that secrecy.of communication by the intelligence Signals i-s maintained '.`6.1In-anelectrica1 communication vsystem comprisinga.movable'intelligencetransferring memloer and power drive-.means for.said mov able.member-means cooperating with said member to guency, .meansito ,compare,saidscpaljate ifre- V .quency .withtheirequency ofsaid Supply,.1neansto, pro.duce a change. in speed orsaidpower `drive means in accordancewith said:comparison,' and code.:controlledv means for .controllingv`said .frequency .varying .means .and .thereby controlling saidintelligence -transferring 4member ,so..that

...communication by .the intelligence signals at a .plurality ofdifferentsp eeds. is .obtainedsat-predegenerating .intelligencesigna-ls, electrical .means tor drivingsaid. scanner, .a v,frequencyregulated alternatingcurrent power` supply for said scanner drive means;means to vary the frequency of said alternating current power supply toproduce a change in speed of the scanner drive means, and a codeoperated switch for controlling said frequency varying means inaccordance with a prearranged code.

HENRY E. HALLBORG.

GILBERT R. CLARK.

REFERENCES CITED The following references are of record in the le ofthis patent:

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